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3^a=5^b=A
a=log3(A)
b=log5(A)
1/log3(A)+1/log5(A)=2
log3(A)+log5(A)=2log3(A)log5(A)
lgA/lg3+lgA/lg5=2lgA/log3*lgA/lg5
lgA(lg5+lg3)=2(lgA)^2
lgA(lg3+lg5-2lgA)=0
lgA=0或2lgA=lg15
A=1或A=√15
A=1时,a=b=0,不符合题设,舍去,所以
A=√15
1年前
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