Question 1103427
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{{{sin(90-x) = cos(x)}}}<br>
You can see this if you think of a right triangle.  In a right triangle, the acute angles are x and 90-x; by the basic definition of the functions in a right triangle, the sine of one acute angle is the cosine of the other, and vice versa.  So sin(90-x) = cos(x) and cos(90-x) = sinx.<br>
Then, by definition, {{{tan(x) = sin(x)/cos(x)}}} and {{{sec(x) = 1/cos(x)}}}<br>
So
{{{(sin(90-x))*(tan(x))*(sec(x)) = (cos(x))*((sin(x)/cosx))*(1/cos(x)) = sin(x)/cos(x) = tan(x)}}}<br>
Answer c.