13.In the diagram, A, B and C lie on the circumference of a circle, centre O. Work out the size of angle ACB. Give a reason for each step of your working

the easiest way to do these would be to solve the equations. if you can solve the equation than you can solve these problems.

the diagram shows you   triangle def with de=4, df=9 and de≠df≠ef.

the sum of the lengths of two triangles' sides are always greater than the length of the third side:

substitute sides lengths:

then 5< ef< 13 (option 3 is true).

def is a scalene triangle with all sides of different lengths (option 5 is true, option 2 is false).

answer: correct choices are 1, 3 and 5

i’m kinda new to precal but your answer should be 21. hope i got it right.

step-by-step explanation: