5(х-3)-2(х-7)=7-7(2х+6)
5х-15-2х+14=7-14х-42
5х-2х+14х=7-42+15-14
17х= -34
х= -2
X²=7
√x²=√7
/x/=√7
x1=√7
x2=-√7
1.sinA=h/AB;
h²=AB²-(AC/2)²=AB²-9;⇒
√(AB²-9)/AB=0.8;⇒
√(AB²-9)=0.8AB;⇒
AB²-9=0,64AB²;⇒
0.36AB²=9;
AB=√9/0.36=3/0.6=5
2.ΔCHB⇒CB=√(CH²+HB²)=√(9+91)=√100=10;
cos(π-α)=-cosα;⇒
cos(∠ABC)=-cos(∠HBC)=-(HB/CB)=-3/10=-0.3;