1) (а-4b)²-8ab-17b=(a²-2•a•4b+4b²)-8ab-17b=a²-8ab+4b²-8ab-17b=a²+4b²-17b
2)-9c²+(3c+b)²-b²=-9c²+(9c²+2•3c•b+b²)-b²=-9c²+9c²+6bc+b²-b²=6bc
3) (5a-6)²-(5a-6)(5a+6)=(5a-6)²-(5a-6)²=0
1/3х=5
х=5:1/3
x=15
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5*3/1=15