Use the identity $(x + a) (x + b) = x^{2} + (a + b) x + a b$ to find the given product:
$(x + 3) (x + 7) .$

x^{2} + 10 x + 21

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x^{3} + 10 x + 11

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x^{2} - 11 x + 21

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x^{2} + 11 x - 21

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Solution

The correct option is A $x^{2} + 10 x + 21$
Given, $(x + 3) (x + 7)$ .

We know, $(x + a) (x + b) = x^{2} + (a + b) x + a b$ .

On comparing we get,
$x = x, a = 3, b = 7$

Thus,
$(x + 3) (x + 7)$
$= (x)^{2} + (3 + 7) x + 3 \times 7$
$= x^{2} + 10 x + 21$ .

Hence, option $A$ is the answer.

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Question 2(i)
Use the identity $(x + a) (x + b) = x^{2} + (a + b) x + a b$ to find the following products:
(x+3)(x+7)

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