tan 6 tan 42 tan 66 tan 78 = 1 prove it
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taking lhs= tan6 tan42 tan66 tan78
now we have to convert it in the form : tan(a)tan(60-a)tan(60+a) =tan3a
so, multiply and divide by tan54 and tan18
therefore we get : tan6 tan(60-6) tan(60+6) tan(18) tan (60-18) tan (60+18)/ tan54 tan18
= tan3(6) tan3(18)/ tan54 tan 18
= tan 18 tan54/ tan18 tan54 =1
hence proofed
now we have to convert it in the form : tan(a)tan(60-a)tan(60+a) =tan3a
so, multiply and divide by tan54 and tan18
therefore we get : tan6 tan(60-6) tan(60+6) tan(18) tan (60-18) tan (60+18)/ tan54 tan18
= tan3(6) tan3(18)/ tan54 tan 18
= tan 18 tan54/ tan18 tan54 =1
hence proofed
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