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15 more than a square of a number is:

x

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:

x

Transferring 8x to the left hand side, we get:

x

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.

X^2 + 15 = 8x

x^2 - 8x + 15 = 0

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

x-5 = 0 | x -3 = 0

x = 5 | x = 3

x^2 - 8x + 15 = 0

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

x-5 = 0 | x -3 = 0

x = 5 | x = 3