а) 3ab = 3ba = a3b = ab3 = b3a = ba3
б) d(-2)3c = -6cd = -6dc = -c6d = -cd6 = -d6c = -dc6
в) x7yz = x7zy = xy7z = xyz7 = xz7y = xzy7 = 7xyz = 7xzy = 7yxz = 7yzx = 7zxy = 7zyx
= y7xz = y7zx = yx7z = yxz7 = yz7x = yzx7 = z7xy = z7yx = zx7y = zxy7 = zy7x = zyx7
г) a4 = 4a
д) ab3 = a3b = 3ab = 3ba = ba3 = b3a
е) 2ak5 = 10ak = 10ka = a10k = ak10 = k10a = ka10
ж) a(-2)bc = -a2cb = -ab2c = -abc2 = -ac2b = -acb2 = -2abc = -2acb = -2bac = -2bca
= -2cab = -2cba = --b2ac = -b2ca = -ba2c = -bac2 = -bc2a = -bca2 = -c2ab = -c2ba
=-ca2b = -cab2 = -cb2a = -cba2
Объяснение:
x+y=85
4x+2y=290
y=85-x
4x+2*(85-x)=290
4x+170-2x=290
4x-2x=290-170
2x=120
x=120/2
x=60