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Multiplication of Polynomials

If 3 x-45 x+7...

Question

If $(3 x - 4) (5 x + 7) = 15 x^{2} - a x - 28$ , then find the value of a.

A

1

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B

- 1

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C

- 2

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D

None of these

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Solution

The correct option is B
- 1

$(3 x - 4) (5 x + 7) = 15 x^{2} - a x - 28$

$3 x (5 x + 7) - 4 (5 x + 7) = 15 x^{2} - a x - 28$
$15 x^{2} + 21 x - 20 x - 28 = 15 x^{2} - a x - 28$
$15 x^{2} + x - 28 = 15 x^{2} - a x - 28$
$x = - a x$
$- a = 1$
So, $a = - 1$

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(3 x - 4) (5 x + 7) = 15 x^{2} - a x - 28

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(3 x - 4) (5 x + 7) = 15 x^{2} - a x - 28

then a = .........

(a x + 2) (b x + 7) = 15 x^{2} + c x + 14

for all values of

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?

Q. Find the value of a if the expression

3 x^{2} + a x - 7

is divisible by (x - 1)

(x + a) (x + b) (x + c) = x^{3} - 10 x^{2} + 45 x - 15

- (a + b + c)

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