Centre of curvature:

• The reflecting surface of a spherical mirror forms a part of a sphere. The sphere’s centre is called as centre of curvature.
• It is represented by the letter C.
• The centre of curvature is not a part of the mirror. It lies outside its reflecting surface.
• The centre of curvature of a concave mirror lies in front of it.
• However, it lies behind the mirror in case of a convex mirror.

Given points A(2,−5) and B(−2,9)
Let the points be P(x,0).
So, AP=PB and AP2=PB2
 ⇒(x−2)²+(0+5)²=(x+2)²+(0−9)²
⇒x²+4−4x+25=x²+4+4x+81
⇒x²+29−4x=x²+85+4x
⇒−4x−4x=85−29
⇒−8x=56

⇒x=−7
Hence, point on the x-axis which is equidistant from (2,−5) and (−2,9) is (−7,0).

Archaeologists reconstruct the past by a study of the artefacts which they unearth such as seals, coins, remains of buildings, clay, pots or burnt grains. Archaeologist reconstruct the past in the following ways:

• Archaeologists excavate the ancient sites. They try to find about the life of the people by studying various unearthed artefacts such as remains of houses, pots, jewellery, coins, agricultural tools, weighs etc.
• Zooarchaeologists study the animal bones and try to find out if these animals were domesticated. For example, Animal bones found at Harappan sites include those of cattle, sheep, goat, buffalo and pig. It show us that the Harappans were aware of these animal.
• Archaeologists try to find about the prevalence of agriculture by finding the remains of burnt grains. Some ways by which they try to find about the agricultural practices is by studying seals and terracotta sculptures. For example, representations on seals and terracotta sculpture indicate that the bull was known, and archaeologists extrapolate from this that oxen were used for ploughing.
• Archaeologists also try to find about social or economic differences amongst people in the past by studying burial sites. When graves contain pottery and ornaments, it indicate that people during that time believed in afterlife.
• Archaeologists try to look for raw material such as stone nodules, whole shells, copper ore; tools; unfinished objects; rejects and waste materials to identify the centres of craft production.
• Religious beliefs of the people can be reconstructed based on the study of seals and coins. In the Harappan Civilisation, some seals depicted rituals while some seals had plat motifs on them indicating nature worship.

[i] Cognitive Disability
The nature of this disability is mental since cognitive domain is related to using mental abilities and achieving results from it.
It is related to impairments in intellectual functioning and adaptive behaviour. Intellectual functioning means person’s ability to plan, comprehend and reason while adaptive behaviour refers to applying social and practical skills in everyday life. Children suffering from dyslexia, learning difficulties, speech disorders, problem in solving math calculations, short span of attention and short of memory are said to have cognitive disability.
Causes of cognitive disability are as follows

• Cognitive impairment may be present at birth and may be genetic or chromosomal or result from complications of pregnancy.
• Chromosomal abnormalities such as Down syndrome, fragile X syndrome.
• Genetic abnormalities such as phenylketonuria, Hunter syndrome etc.
• Prenatal drug and infections and exposure to alcohol.
• Lack of oxygen during labour pain or birth.

[ii] Intellectual Disability
The nature of this disability is also mental since the intellectual domain is related to using the capacity of the mind. It is a disability characterised by significant limitations in both intellectual functioning and in adaptive behaviour. This is characterised by low intelligence quotient score (under 70) and significant problems in the ways learners adapt to new situations. It is different from cognitive because cognitive is a broad concept while intellectual disability is specific in nature.
Causes of intellectual disability are as follows

1. Genetic Conditions These include things like Down syndrome and fragile X syndrome.
2. Problems during Pregnancy This can interfere with fetal brain development.
3. Alcohol or Drug Use may also cause intellectual disability.
4. Problems during Childbirth Like if a baby is deprived of oxygen during childbirth or born extremely premature.

To add an animated image in HTML is quite easy. You need to use the <image> tag with the src attribute. The src attribute adds the URL of the image. Also, set the height and width of the image using the height and width attribute. The HTML <marquee> tag defines a scrolling text area in the HTML document that moves across the page in a horizontal or vertical direction. By default, text found within the <marquee> tag will scroll from right to left. The <marquee> tag has been deprecated in HTML5 and should no longer be used.

Wrought Iron is the purest form of iron. It contains 0.12 to 0.25% carbon and is thus the purest form of iron.

Learning is the process of acquiring new understanding, knowledge, behaviors, skills, values, attitudes, and preferences. There are three main types of learning: classical conditioning, operant conditioning, and observational learning. Both classical and operant conditioning are forms of associative learning, in which associations are made between events that occur together.

Learned helplessness, in psychology, a mental state in which an organism forced to bear aversive stimuli, or stimuli that are painful or otherwise unpleasant, becomes unable or unwilling to avoid subsequent encounters with those stimuli, even if they are “escapable,” presumably because it has learned that it cannot control the situation.

Learned helplessness occurs when an individual continuously faces a negative, uncontrollable situation and stops trying to change their circumstances, even when they have the ability to do so. For example, a smoker may repeatedly try and fail to quit. Three components are necessary for learned helplessness to be present: contingency, cognition, and behavior. Learned helplessness theory is the view that clinical depression and related mental illnesses may result from such real or perceived absence of control over the outcome of a situation.

Schedules of reinforcement are the precise rules that are used to present (or to remove) reinforcers (or punishers) following a specified operant behavior. These rules are defined in terms of the time and/or the number of responses required in order to present (or to remove) a reinforcer (or a punisher).

There are four basic types of intermittent schedules of reinforcement and these are:

• Fixed-Ratio (FR) Schedule.
• Fixed Interval (FI) Schedule.
• Variable-Ratio (VR) schedule.
• Variable-Interval (VI) schedule.

Observational learning describes the process of learning through watching others, retaining the information, and then later replicating the behaviors that were observed. ... A tremendous amount of learning happens through this process of watching and imitating others. In psychology, this is known as observational learning. Observational learning occurs through observing negative and positive behaviors. Bandura believes in reciprocal determinism in which the environment can influence people's behavior and vice versa. For instance, the Bobo doll experiment shows that the model, in a determined environment, affects children's behavior.

Operant conditioning (also called instrumental conditioning) is a type of associative learning process through which the strength of a behavior is modified by reinforcement or punishment. It is also a procedure that is used to bring about such learning. ... Operant behavior is said to be "voluntary". Skinner in his theory of operant conditioning. ... The reward is a reinforcing stimulus. Skinner showed how positive reinforcement worked by placing a hungry rat in his Skinner box. The box contained a lever on the side, and as the rat moved about the box, it would accidentally knock the lever.

The one's digit of the square of a no. could be found using the the unit digit of the no. itself .So the one's digits of given no.s are :

1. 1234    : 6
2. 26387 ; 9
3. 52698 ; 4
4. 21222  ; 4
5. 9106    ; 6
6. 99880 ; 0

There are three main types of learning: classical conditioning, operant conditioning, and observational learning. Both classical and operant conditioning are forms of associative learning, in which associations are made between events that occur together.

Vladimir Ilyich ​Ulyanov, better known as Lenin, was a Russian communist revolutionary and politician. He served as the first leader of the Russian Soviet Socialist Republic after its formation in the Russian Revolution of 1917.

Lenin played a very important role in the Russian Revolution of 1917.

1.He was the leader of the Bolsheviks who conducted the Revolution. 
2. Under his leadership, the revolutionary government introduced radical land reforms and transformed the country into a socialist state.
3. He led the Bolsheviks to victory in the Russian Civil War from 1917 to 1922.
4. He introduced the New Economic Policy which was a mixed economic system with a leading role for the state. It started the process of industrialisation and recovery from the Civil War.
5. In 1922, just before Lenin's death, the Russia joined other terrirtories of the former Tsar's empire to form the Soviet Union.

Let the numbers be x and 3x 

Then, 

         (x+5)/  (3x+5) ​=21​

          ⇒2x+10=3x+5

          ⇒x=5 

Hence, the numbers are 5 and 15 

∴ Sum of numbers = 20

In geography, a plain is a flat, sweeping landmass that generally does not change much in elevation. Plains occur as lowlands along valleys or on the doorsteps of mountains, as coastal plains, and as plateaus or uplands.