AS Level Maths Q HELP

Hiya, the length of the are of the circle is, C=rθ. The perimeter of the sector would be two times the length of the radius + the length of the arc = 40 (as given). This written as an expression would be, 2r + C = 40 , which would be 2r + rθ = 40. The area of the sector is, A = 1/2 r^2 θ . rearrange the equation of the area to subsitute θ. you should get the expression. θ = 2A/r^2 , which you sub into the other equation to get 2r + 2A/r =40. rearranging this to get the equation above


hope i helped