7a²(a-x)+(6a²-ax)(x-a)=7a³-7x+6a²x-6a³-ax²-a²x=a³-7x+5a²x-ax².
11b²(3b-y)-(6y-3b²)(y-3b)=11b³-11b²y-6y²+18by+3b²y-9b³=2b³-8b²y-6y²+18by.
Arccos(x)`=-1/(√(1-x²)
arccos²(x)`=-2*arccos(x)/√(1-x²)
1/arccos²(x)=(1`*arccos²(x)-1*arccos²(x)`)/arccos⁴(x)=
=(0-(-2*arccos(x)/√(1-x²))/arccos⁴(x)=2*arccos(x)/(arccos⁴(x)*√(1-x²)).
Корень 81 / корень 361 + корень 1/4 =
9/19+1/2= 37/38