Expand the following: $(3 a - 5 b - 7 c)^{2}$

9 a^{2} + 25 b^{2} + 49 c^{2} - 30 a b + 40 b c - 42 c a

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9 a^{2} + 25 b^{2} + 49 c^{2} - 30 a b + 50 b c - 42 c a

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9 a^{2} + 25 b^{2} + 49 c^{2} - 30 a b + 60 b c - 42 c a

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9 a^{2} + 25 b^{2} + 49 c^{2} - 30 a b + 70 b c - 42 c a

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Solution

The correct option is D $9 a^{2} + 25 b^{2} + 49 c^{2} - 30 a b + 70 b c - 42 c a$
$(3 a - 5 b - 7 c)^{2}$
Using, $(a + b + c)^{2} = a^{2} + b^{2} + c^{2} + 2 a b + 2 b c + 2 c a$
$= (3 a)^{2} + (- 5 b)^{2} + (- 7 c)^{2} + 2 \times 3 a \times (- 5 b) + 2 \times (- 5 b) \times (- 7 c) + 2 \times (- 7 c) \times (3 a)$
$= 9 a^{2} + 25 b^{2} + 49 c^{2} - 30 a b + 70 b c - 42 c a$

Suggest Corrections

Similar questions

49 a^{2} + 70 a b + 25 b^{2}

9 a^{2} - 30 a b + 25 b^{2}

(2 a - 5 b - 4 c)^{2}

4 a^{2} + 25 b^{2} + 16 c^{2} - 20 a b + 40 b c - 16 c a

- 5 a^{2} - 2 a + 1

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8 a - 7

9 a^{2} + \frac{1}{9 a^{2}} - 2 - 12 a + \frac{4}{3 a}

Factorise:

$9 a^{2} + \frac{1}{9 a^{2}} - 2 - 12 a + \frac{4}{3 a}$

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