2.10 b) a² -ac +bc -ab =a(a -c) -b(a -c) =(a -c)(a -b)
(a+2b)/3(a -b) -(3c -a)/2(a-c) +(a² -bc)/(a -c)(a -b) =
=(2(a-c)(a+2b) -3(a-b)(3c-a) +6(a²-bc)) /6(a-c)(a-b) =
=(2(a²+2ab-ac-2bc) -3(3ac-a² -3bc+ab) +6a² -6bc) /6(a -c)(a -b) =
=(2a²+4ab -2ac-4bc -9ac +3a² +9bc -3ab +6a² -6bc) /6(a -c)(a -b) =
=(11a² +ab -11ac -bc) /6(a -c)(a -b) =
=11a(a -c) +b(a -c)) /6(a -c)(a -b) =
=(a -c)(11a +b) /6(a -c)(a -b) =
=(11a +b) /6(a -b) =(11/6 -1) /6(1/6 +1) =
=(11-6)/6 : 6*7/6 =5/6 : 7 =5/6 *1/7 =5/42
Формула суммы=((a1+d(n-1))2)*n
((-10+10(5-1))/2)*5=75
Ответ: 75 сумма первых пяти членов
5-6cos^2a
1) cos^2a=1-(-3/8)^2
2) -6cos^2a=-330/64
3) 5-330/64= (320-330)/64=-5/32
A9=22.2
a23=-41.8
d=?
d=(-41.8-22.2)/14=-64/14=-32/7
4-2(5-4х)=-х+1
4-10+8х=1-х
8х+х=-4+10+1
9х=15
х=15:9
х=5:3
х=1⅔