а. (2x-7y)^2+(3x +4y)^2-(3x+y)(3x-y)=4x^2-28xy+49y^2+9x^2+24xy+16y^2-9x^2+y^2=4x^2-4xy+66y^2=2(2x^2-2xy+33y^2)
б. 5(a-4b)(4b+a)+(a-4b)(-4b+a)+(a+4b)^2=5(a^2-16b^2)-(16b^2-a^2)+a^2+8ab+16b^2= 5a^2-80b^2-16b^2+a^2+a^2+8ab+16b^2=7a^2+8fb-80b^2
15*2/15*(-2) - 2*(-2) + 15*(2/15)^2 - 2*2/15 = -4 - (-4) + 4/15 - 4/15 = -4+4 + 4/15 - 4/15 = 0
Х=-0,00153, аб. погр.=|-0,0015281-(-0,00153)|=0,0000019, отн. погр.=0,0000019/0,00153=0,00124...
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