Quadratic graph; solving equations.

**vanklik** · January 27th 2010, 01:20 PM

Hi, I hope someone will help me! I've got a graph of x2+3x=8 (quadratic). By drawing a suitable straigt line on the graph, I need to solve the equation: x2+2x-4=0 (quadratic) How do I draw the second graph without solving the equation first?
Thank you for your help!

**Archie Meade** · January 27th 2010, 02:33 PM

Originally Posted by vanklik

Hi, I hope someone will help me! I've got a graph of x2+3x=8 (quadratic). By drawing a suitable straigt line on the graph, I need to solve the equation: x2+2x-4=0 (quadratic) How do I draw the second graph without solving the equation first?
Thank you for your help!

Hi vanklik,

$x^2+2x-4=(x^2+3x-8)-(x-4)$

Therefore you can solve $x^2+2x-4=0$ by solving $(x^2+3x-8)-(x-4)=0$

In other words, by finding where the line $x-4$ crosses the curve $x^2+3x-8$

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