若α=20° 则根号下(tanα-1)^2如题,计算!

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若α=20°则根号下(tanα-1)^2如题,计算!若α=20°则根号下(tanα-1)^2如题,计算!若α=20°则根号下(tanα-1)^2如题,计算!0°An=1/(n+1)(n+3)=(1/2

若α=20° 则根号下(tanα-1)^2如题,计算!
若α=20° 则根号下(tanα-1)^2
如题,计算!

若α=20° 则根号下(tanα-1)^2如题,计算!

An=1/(n+1)(n+3)
=(1/2)*2/(n+1)(n+3)
=(1/2)[(n+3)-(n+1)]/(n+1)(n+3)
=(1/2)[(n+3)(n+1)(n+3)-(n+1)(n+1)(n+3)]
=(1/2)[1/(n+1)-1/(n+3)]
所以Sn=(1/2)[1/2-1/4+1/3-1/5+……1/n-1/(n+2)+1/(n+1)-1/(n+3)]
=(1/2)[1/2+1/3-1/(n+2)-1/(n+3)]
=(5n²+13n)/(12n²+60n+72)