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December 25, 2014

December 25, 2014

Posted by **Neil** on Friday, September 24, 2010 at 1:59pm.

4x² - 7y² = 21

x² + 2y² = 99

- Algebra -
**Ron**, Friday, September 24, 2010 at 4:45pm4x² - 7y² = 21 (eq1)

x² + 2y² = 99 (eq2)

--> eq1-4*eq2

-->

4x² - 7y² = 21 (eq1)

-4x² - 8y² =- 396 -4*(eq2)

___________________

-15y²=-375 (eq3)

--> y²=25 (eq4)

Back sub to get

x² + 2(25) = 99

--> x² =99-50

--> x² =49 (eq5)

x =(+/-)sqrt(49) (eq6)

###############

# x =(+/-)7 # (eq7)

###############

y =(+/-)sqrt(25) (eq8)

###############

# y =(+/-)5 # (eq9)

###############

You could also use Matrix Methods

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