Triangle ABC is similar to triangle DEF. Find the measure of side DE. Round your answer to the nearest tenth if necessary.
8
B
F
31
E
Ď
13-7
D

53.1

Step-by-step explanation:

They're equal, so 8 = 31 and 13.7 = x

8/31 = 13.7/x

31(13.7) / 8 = 53.0875

Round your answer to nearest tenth to get 53.1

c.

step-by-step explanation:

she should of added 9^2 and 12^2. that is because it is a^2+b^2=c^2. c^2 is the hypotenuse and should always be bigger than the other two numbers. which is why she should of added 9 squared and 12 squared together instead of 15 squared.

let's call the solutions x₁ = (5 - 2√7)/3 and x₂ = (5 + 2√7)/3

then the equation is (x-x₁)(x-x₂) = 0

if you fill that in you get a lot of numbers which you can recognize as ax²+bx+c=0.

step-by-step explanation:

you can see that a=1 (there is just an x²)

b = (-5 -2√7 + 2√7 - 5)/3 = -10/3

c = -2√7)/3 ) * (-5+2√7)/3) = -1/3

so your answer is 3x^2 – 10x – 1 = 0