book Maths Puzzle Numerical Ability

x^2+5x-6

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book Other Question

Quadratic equations:

Find two possitive numbers that differ by 2 and have a producy of 20.

The answer is -1 + squareroot of 21 and 1 + squareroot of 21.

How do I at the answer. (need steps)
problem:
the area of a circle is 25 meters. find the radius of the circle.
i solved to this point.
7.96 m (squared)= r (squared)

the books says answer is r=2.82

i need to understand the step on how they got the answer
thanks.