Answer:
Sin theta = Perpendicular/Hypotenuse = a/√(a^2+b^2)
cos theta = 1- sintheta = 1- a/√(a^2+b^2)
Tan theta = sin/cos = tan = sin/1-sin
= a/√(a^2+b^2)/√(a^2+b^2)-a/(a^2+b^2)
= a/√(a^2+b^2) × (a^2+b^2)/(a^2+b^2)-a
= a/(a^2+b^2)-a
So cosec theta = inverse of sine theta = (a^2+b^2)/a
Sec theta = inverse of cos theta = a-(a^2+b^2)/a
Cotan theta = inverse of tan theta = (a^2+b^2)-a/a
Hope it helps