I already know how to do it... I just want to know what the importance is...
for example...
Sin with respect to tan is sin/(1-sin^2)^(1/2)
W/ respect to sec... 1/(i-sin^2)^(1/2)...
and so on..
The main cofunctions are for expressing values in two dimensions, since Trigonometric functions are circular functions. The reciprocal and ratio forms of these functions allow for some simpler terms when writing equations or functions for specific topics which use Trigonometry. Note also that vectors may be in different directions and by that be at an angle to eachother; this justifies the use of Tangent to help in quantifying or describing the angle (remember when you learned that in a plane the the product of the slopes of perpendicular lines is negative one?).