Log(3)4=a
log(3)5=b
log(3)80=log(3)(5*4²)=log(3)5+2log(3)4=a+2b
log(3)144=log(3)(3²*4²)=2+2a
<span>= 9а^2-42ab+49b^2+42ab= 9a^2+49b^2
= a^2+2ab-2ac-2bc+b^2+c^2
</span>
7^2=7×7=49
12^3=12×12×12=144×12=1728
Надеюсь, принцип понятен.
(b+c-2a)(c-b)+(c+a-2b)(a-c)-(a+b-2c)(a-b)=
=bc+c²-2ac-b²-bc+2ab+ac+a²-2ab-c²-ac+2bc-a²-ab+2ac+ab+b²-2bc=
=(bc-bc+2bc-2bc)+(ac-ac+2ac-2ac)+(ab-ab+2ab-2ab)+(a²-a²+b²-b²+c²-c²)≡0.
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