Tgx * ctgx = 1
ctgx = 1/tgx ===>
<span>2ctgx + ctgx = 3ctgx </span>
2x+1=0
2x=-1
x=-0.5 ...............................
∛9-∛7*(∛81+∛63)+∛49 = ∛9-(∛7*81)+(∛7*63)+∛49 = ∛(3^2)-3*∛(7*3)+∛(7^2*3^2)+∛(7^2) = ∛9*(1+∛49) - ∛49*(3*∛3+1)
(√15-8)*(√15-8)=√7*√7=√7*7=√49=7