Find the product $(a + b) (a - 2 b)$ , when $a = 1$ , $b = 2$ .

8

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- 9

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Solution

The correct option is D $- 9$
$= (a + b) (a - 2 b) = a \times a + b \times (- 2 b) + b \times a + a \times (- 2 b)$
$= a^{2} - 2 b^{2} - a b$
$a = 1, b = 2$
$= 1 - 2 \times 2^{2} - 1 \times 2$
$= - 9$

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Find the product (a+b)(a−2b), when a=1, b=2.

The correct option is D −9=(a+b)(a−2b)=a×a+b×(−2b)+b×a+a×(−2b) =a2−2b2−aba=1,b=2 =1−2×22−1×2 =−9

Find the product $(a + b) (a - 2 b)$ , when $a = 1$ , $b = 2$ .

The correct option is D $- 9$
$= (a + b) (a - 2 b) = a \times a + b \times (- 2 b) + b \times a + a \times (- 2 b)$
$= a^{2} - 2 b^{2} - a b$
$a = 1, b = 2$
$= 1 - 2 \times 2^{2} - 1 \times 2$
$= - 9$