Question

先化简,在求值4a/a^2-4-2/a+2其中a=√2+2

Answer 1

4a/a^2-4-2/a+2

=4a/(a+2)(a-2)-2/(a+2)

=[4a-2(a-2)]/(a+2)(a-2)

=4/(a+2)(a-2)

=4/(√2+2+2)(√2+2-2)

=4/√2(√2+4)

=4/(2+4√2)

=2/(1+2√2)

=2(2√2-1)/(2√2+1)(2√2-1)

=(4√2-2)/(8-1)

=(4√2-2)/7

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