1.4×1.5=2.1
1.8+2.1=3.9
1.8×1.2=2.16
1.5×1.4=2.1
2.16-2.1=0.06
3.9÷0.06=65
по формуле приведения sin144=sin36
sin36cos54+cos36sin54=sin(36+54)=sin90=1
Sin7x+sin3x=3cos2x;⇒2sin(7x+3x)/2·cos(7x-3x)/2=3cos2x;⇒
2sin5x·cos2x-3cos2x=0;⇒cos2x(2sin5x-3)=0;
cos2x=0;⇒2x=π/2+kπ;k∈Z;⇒x=π/4+kπ/2;k∈Z;
2sin5x-3=0;⇒sin5x=3/2;3/2>1;-решений нет,т.к
-1≤sinx≤1;
(x-3√x-4)/(√x+1)=(√x-4)(√x+1)/(√x+1)=√x-4
D=9+16=25
√x=t
t12=(3+-5)/2=4 -1