Question

Which two equations would be most appropriately solved by using the quadratic formula? Select each correct answer. (x+8)(x+9)=0 5x2+7x=15 0.25x2+0.8x−8=0 (x−3)2=36

Answer 1

Answer:

 $5x^{2} +7x =15$

 $0.25x^{2} +0.8x-8=0$

Step-by-step explanation:

Given equations : $(x+8)(x+9)$

                              $5x^{2} +7x =15$

                              $0.25x^{2} +0.8x-8=0$

                              $(x-3)^{2}=36$

Solution:

A)  $5x^{2} +7x =15$

It is not appropriately solved by using the quadratic formula because the solution is direct

The solution is x=-8 and x=-9

B)  $5x^{2} +7x =15$

⇒ $5x^{2} +7x-15=0$

 It is appropriately solved by using the quadratic formula because the solution is not direct

C) $0.25x^{2} +0.8x-8=0$

It is appropriately solved by using the quadratic formula because the solution is not direct

D) $(x-3)^{2}=36$

⇒$(x-3)^{2}=6^2$

⇒$(x-3)=6$

⇒$x=6+3$

⇒$x=9$

It is not appropriately solved by using the quadratic formula because the solution is direct.

Hence Option B and C are the two equations would be most appropriately solved by using the quadratic formula.

Answer 2

Correct Answers:
0.25x²+0.8x-8=0
5x²+7x=15

Reasons: 0.25x²+0.8x-8=0 is already in standard quadratic form, so you can just use the numbers in the quadratic formula.
5x²+7x=15 is also in standard form; all you have to do is change it from the original equation to proper standard form by moving the 15 to the other side. Thus, that equation is changed to 5x²+7x-15=0. I hope this helps you. ☺