Answer:
when x = 39.25, y = 2.75
when x = 2.75, x = 39.25
Step-by-step explanation:
use substitution method
x+y = 42 ------ (1)
xy = 108 ------ (2)
from (1) ,
x+y = 42
y = 42-x ------ (3)
substitute (3) into (2)
xy = 108
x( 42-x ) = 108
42x - x² = 108
-x² + 42x - 108 = 0
x² - 42x + 108 = 0
use the following formula to solve the value of x:
[tex]i) \: x = \frac{ - b + \sqrt{ {b}^{2} - 4ac } }{2a} \: \\ ii) \: x = \frac{ - b - \sqrt{ {b}^{2} - 4ac } }{2a} [/tex]
a = 1
b = -42
c = 108
[tex]i) \: x = \frac{ - b + \sqrt{ {b}^{2} - 4ac} }{2a} [/tex]
[tex]x = \frac{ - ( - 42) + \sqrt{( - 42) {}^{2} - 4(1)(108)} }{2(1)} [/tex]
[tex]x = \frac{42 + \sqrt{1764 - 432} }{2} [/tex]
[tex]x = \frac{42 + \sqrt{1332} }{2} [/tex]
[tex]x = \frac{42 + 6 \sqrt{37} }{2} [/tex]
[tex]x = 21 + 3 \sqrt{37} [/tex]
[tex]x = 39.25[/tex]
[tex]ii) \: x \: \frac{ - b - \sqrt{ {b}^{2} - 4ac} }{2a} [/tex]
[tex]x = \frac{ - ( - 42) - \sqrt{( - 42) {}^{2} - 4(1)(108} }{2(1)} [/tex]
[tex]x = \frac{42 - \sqrt{1764 - 432} }{2} [/tex]
[tex]x = \frac{42 - \sqrt{1332} }{2} [/tex]
[tex]x = \frac{42 - 6 \sqrt{37} }{2} [/tex]
[tex]x = 21 - 3 \sqrt{37} [/tex]
[tex]x = 2.75[/tex]
the 2 values of x are x = 39.25 and x = 2.75
substitute x = 39.25 into (3)
y = 42-x
y = 42-39.25
y = 2.75
substitute x = 2.75 into (3)
y = 42-x
y = 42-2.75
y = 39.25
when x = 39.25, y = 2.75
when x = 2.75, x = 39.25
