Question

Solve for x.

5x2 – 45 = 0

A.
{3}

B.
{3, –3}

C.
{9, –9}

D.
{9}

Answer 1

Hi there! 5x²-45=0, add 45 to both sides, 5x²-45+45=0+45=5x²=45. Divide both sides by 5, 5x²/5=45/5, 45/5=9. So, we have x²=9. we have to find the square root of 9. The square root of 9 is 3*3 because 3*3=9. We have two solutions, the first solution is x=3 and the other solution is x=-3. X=3 and x=-3 can be combined and we get {3,-3}. Therefore, your answer is B. {3,-3}

Answer 2

5x^2-45=0
factor 5 out
5(x^2-9)=0
diff 2 perfec squares
5(x-3)(x+3)=0
set zero
x-3=0
x=3

x+3=0
x=-3

x=-3 or 3

B