Q 1 :

The expression tanA1-cotA+cotA1-tanA can be written as:                [2013]

  • sinAcosA+1

     

  • secAcosecA+1

     

  • tanA+cotA

     

  • secA+cosecA

     

(2)

Given expression can be written as

sinAcosA×sinAsinA-cosA+cosAsinA×cosAcosA-sinA

=1sinA-cosA{sin3A-cos3AcosAsinA}

 a3-b3=(a-b)(a2+ab+b2)

=sin2A+sinAcosA+cos2AsinAcosA=1+secAcosecA



Q 2 :

Given both θ and ϕ are acute angles and sinθ=12,cosϕ=13, then the value of θ+ϕ belongs to            [2004]

  • (π3,π2]

     

  • (π2,2π3)

     

  • (2π3,5π6]

     

  • (5π6,π]

     

(2)

Given: sinθ=12 and θ is acute angle

 θ=π6

Also given, cosϕ=13 and ϕ is acute angle.

 0<13<12

cosπ2<cosϕ<cosπ3 or π3<ϕ<π2

 π3+π6<θ+ϕ<π2+π6 or π2<θ+ϕ<2π3

θ+ϕ(π2,2π3)