Let x, y be greater than zero, and 2x + 5Y = 20. If M = old x + old y, then the maximum value of M is?

Let x, y be greater than zero, and 2x + 5Y = 20. If M = old x + old y, then the maximum value of M is?

Because 2x + 5Y=
So y = (20-2x) / 5 = 4-2 / 5x
XY=-2/5X^2+4X
=-2/5(X^2-10X)
=-2/5(X-5)^2+10
XY max = 10
Mmax = lgx + lgY
=lg(XY)
=lg10
=1

In △ ABC, cosa = - 513, CoSb = 35. (I) find the value of sinc; (II) let BC = 5, find the area of △ ABC

(1) from cosa = - 513, Sina = 1213, from CoSb = 35, SINB = 45. So sinc = sin (a + b) = sinacosb + cosasinb = 1665. (2) from sine theorem, AC = BC × sinbsina = 5 × 451213 = 133

Let Z be a complex number
What is Z
For example, what is the absolute value of the complex number - 4-6i
What is the absolute value of 4 + 6I

If z = a + bi, then | Z | = (a ^ 2 + B ^ 2) ^ 0.5 (| Z | is the module of Z, not the absolute value)
So the modules of - 4-6i and 4 + 6I are 2 * 13 ^ 0.5