PLEASE HELP WILL MARK BRAINLIEST! Also please explain the answer

Each triangle is a right triangle.

Step-by-step explanation:

You can see each one has one 90 degree corner.

13. True

14. True

15. False

Step-by-step explanation:

By using the Pythagorean Theorem a^2+b^2=c^2, you can evaluate whether or not the triangles are right triangles.

13. 8^2+15^2=17^2   ->  64+225=289  -> TRUE

14. 50^2+120^2=130^2  -> 2500+14400=16900  -> TRUE

15. 12^2+35^2=36^2  -> 144+1225 =/=1296 -> FALSE

(b) 240

step-by-step explanation:

first, we use the pythagorean formula using the given side lengths to find x. then we use x to find the side lengths. then we add the side lengths to find the perimeter.

pythagorean theorem formula:

a^2 + b^2 = c^2

(x - 20)^2 + (x - 40)^2 = x^2

x^2 - 40x + 400 + x^2 - 80x + 1600 = x^2

x^2 -120x + 2000 = 0

(x - 100)(x - 20) = 0

x - 100 = 0 or x - 20 = 0

x = 100 or x = 20

we see that the solution x = 20 must be discarded because it will give a negative side length and a side length of 0. the only valid solution is x = 100.

perimeter = sum of the lengths of the sides

perimeter = x + x - 20 + x - 40

perimeter = 3x - 60

replace x with 100.

perimeter = 3(100) - 60

perimeter = 300 - 60

perimeter = 240