Question

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Question- The difference of the square of a number and three times the sum of the number and 7 is more than the product of that number and 15.
Select the inequality that can be used to determine the unknown number.

A. x2 + 3x ≥ 15 + x
B. x2 - 3x + 7 ≥ 15x
C. x2 - 3x - 21 > 15x
D. x2 - 3x + 21 > 15 + x

Answer 1

In my own understanding, I would say b

Answer 2

C.
`x^2 - 3x -21 > 15x`

Explanation:

Let x be the unknown number,

So, the square of the number =
`x^2`

Three times of the sum of number and 7 = 3(x+7),

Also, the product of the number and 15x,

Thus, The difference of the square of a number and three times the sum of the number and 7 is more than the product of that number and 15.

⇒
`x^2-3(x+7) > 15x` ( sign '>' is used for more than )

⇒
`x^2-3x-21 > 15x` ( Apply distributive property on left side )

Hence, option 'C' is correct.