1.

Why is the 2nd WRONG?​

Answer»

dear user

In first

A=

\pi( {r1}^{2} - {r2}^{2} ) = \pi(r1 - r2)(r1 + r2)

This is from the formula

a^2-b^2=(a+b)(a-b)

In second

A=

\pi( {r2 - r1)}^{2} = \pi( {r1}^{2} + {r2}^{2} - 2r1r2)

This is from formula

(a-b)^2=a^2+b^2-2ab

{u may have learn in JUNIOR CLASSES)

so they can't be same


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