Maths ! the angles in triangle abc are given in degrees, prove that ab=ac

First, find out the value of x to confirm if they are really true. 

We know that all the interior angles of a triangle equal to 180 degrees. 

4x+5x-8+3x+20=180 
12x=180-12 
12x=168
x=168/12 
x=14 

Put in these values of to find if AB=AC. 

(4×14)(3×14+20)=(4×14)(5×14-8) 

Solve for LHS first, 

(4×14)(3×14+20) = 56×62 

=3472 

Solve for RHS next, 

(4×14)(5×14-8) = 56×62

=3472

Since LHS=RHS, AB is also equal to AC. 

Hope I helped :)