4 sin^2(x) + 8 cos(x) = 7

1 = cosē(x)+sinēx

sinē(x) = 1-cosē(x)

we use this and replace sinē(x) with 1-cosē(x)

4(1-cosē(x))+8cos(x) = 4-4cosē(x)+8cos(x)

-4cosē(x)+8cos(x)+4 = 7

replace

[cos(x)=t] and multiplicate with -1

4tē-8t-4 = -7 <--> t1= 1/2 t2=3/2

t = cos(x),

cos(x1)=1/2

cos(x2)=3/2

x1=pi/3 + n *2pi or x1=pi - pi/3 + n *2pi but the second one is wrong ? why ?

Cos(x2) > 1 = dont work