Starting with {{MATH_126}} we differentiate both sides of the equation with respect to {{MATH_127}} to obtain {{MATH_128}} Applying the sum rule we get that {{MATH_129}} Let's examine each of these terms in turn. To start {{MATH_130}} On the other hand {{MATH_131}} is somewhat different. Here you assume that {{MATH_132}}, on some interval {{MATH_133}}, and hence by the chain rule {{ENV_134}} Considering the final term {{MATH_135}}, we assume that {{MATH_136}}, on some interval {{MATH_137}}. Hence {{ENV_138}} Putting this all together we are left with the equation {{MATH_139}} At this point, we solve for {{MATH_140}}. Write {{ENV_141}}