Question

25x^2cosx+x^2=225cosx+9

Answer 1

x²(25cosx+1)-9(25cosx+1)=0
(25cosx+1)(x-3)(x+3)=0
25cosx+1=0⇒25cosx=-1⇒cosx=-0,04⇒x=+-(π-arccos0,04)+2πn
x-3=0⇒x=3
x+3=0⇒x=-3