<span>(4c+2)(3c-5)=12с</span>²<span>- 20
12c</span>²-20c+6c-10=12c²-20
-20c+6c-10=-20
-14c=-20+10
-14c=-10
c=10/14
c=5/7
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(4c+2)(3c-5)=12c²-20c+6c-10=12c²-14c-10
1. Cos(2arccos4/5)=2cos²(arrcos4/5)-1=2*4/5*4/5-1=32/25-1=7/25
<span>2.cos(pi-2arccos4/5)=-cos(2arccos4/5)=-7/25</span>
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Y=0
-3X-7=0
-3X=7
X=- 7/3
X=-2 1/3