Answers

2014-04-04T11:29:07+08:00
Let x be the number.

15 more than a square of a number is:
x²+15

Eight times the number is:
8*x or 8x

The identifier "is" on the question means the two are equal, therefore, we make an equation:
x²+15=8x

Transferring 8x to the left hand side, we get:
x²-8x+15=0
We did this step because it is easier to find the roots in this form.

Factoring:
(x-5)(x-3)=0

x-5=0  , therefore x=5 |||  x-3=0, therefore x=3

So we have two solutions.

Let's check if they're both correct. We will substitute the values that we got on the first equation we did.

If x is 5:
(5)²+15=8(5)
25+15=40
40=40
The solution x=5 is correct.

If x=3:
(3)²+15=8(3)
9+15=24
24=24
The solution x=3 is also correct.

Hope that helps.
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2014-04-06T21:30:49+08:00
X^2 + 15 = 8x
x^2 - 8x + 15 = 0
(x-5) (x-3) = 0
x-5 = 0  | x -3 = 0
x = 5     | x = 3
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