Calc Problems

Missed a conference, need help with a couple of problems tracing.?

What number is a main root of more than eight times the number by the largest amount? # 2 The illumination at a point is inversely proportional to the square of the distance from the point of the light source and directly proportional the intensity of the source of light. If light sources are two feet apart s and their intensities are I1 and I2, respectively, at what point between them the sum of its illuminations have a minimum? I really do not have a clue where to start, thanks for your help.

1. y = √ x – 8x Find dy / dx = 0 then set y = x ^ 1 / 2 – 8x dy / dx = 1 / 2 x ^ -1 / 2 to 8 dy / dx = 1 / (2 √ x) – 8 = 0 1 / (2 √ x) = 8.1 cross multiply 16 √ √ x = 1 x = 1 / 16 x = 1 / 256

Pre-calc problems 3-5 part 1.mp4