Sina+cosa=tana(0

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Sina+cosa=tana(0Sina+cosa=tana(0Sina+cosa=tana(0tana=sina+cosa=√2sin(a+π/4)∵0<a<π/2∴π/4<a+π/4<3π/4∴1

Sina+cosa=tana(0
Sina+cosa=tana(0

Sina+cosa=tana(0
tana = sina+cosa = √2sin(a+π/4)
∵ 0<a<π/2
∴ π/4<a+π/4<3π/4
∴ 1<√2sin(a+π/4)≤√2
∴ 1<tana≤√2
∴ π/4<a≤arctan√2