[" 4.If "sec(phi+alpha)+sec(phi-alpha)=2sec phi" ,prove that,"],[cos phi=+-sqrt(2)cos(alpha)/(2)" ."]

If sec(phi+alpha) + sec (phi-alpha) = 2 sec phi , prove that cos phi = pm sqrt(2) "cos"(alpha)/(2) , ( phi ne (pi)/(2)) .

If sec(phi+alpha)+sec(phi-alpha)=2secphi show that cosphi=+-sqrt2cosfrac{alpha}{2}

If sec(x+alpha)+sec(x-alpha)=2sec x, prove that cos x=+-sqrt(2)cos((alpha)/(2))

If sec(theta+alpha)+sec(theta-alpha)=2sec theta, prove that cos theta=+-sqrt(2)(cos alpha)/(2)

If sec(theta+alpha)+sec(theta-alpha)=2sec theta and cos alpha!=1 , prove that cos theta=+-sqrt"cos"(alpha)/2

If sec(theta+alpha)+sec(theta-alpha)=2sec theta then show that cos^(2)theta=1+cos alpha

If sec(theta+alpha)+sec(theta-alpha)=2sec theta then show that cos^(2)theta=1+cos alpha

tan phi cos ec phi=sec phi

If x=sec phi-tan phi and y=cos ec phi+cot phi then

if tan^(alpha)=cos^(2)phi-sin^(2)phi then prove that cos^(alpha)-sin^(2)alpha=tan^(2)phi