The answer is .5 cm. I hope it’s right
4:30 hours ..............
D/dx ( cos (4x)) = - sin (4x) · d/dx ( 4x) = - 4 sin (4x)
let x be how far up the wall ladder reaches
by Pythagoras theorem
x^2+5^2=13^2
x^2 =(13^2)-(5^2)
x= square root of 144
x= 12 or x =-12(rej,x>0)
hence ladder reaches 12 foot up the wall
