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Let$${f}{\left({\mathtt{x}}\right)} = {{\mathtt{x}}}^{{\mathtt{2}}}{\mathtt{\,-\,}}{\mathtt{2}}{\mathtt{\,\times\,}}{\mathtt{x}}{\mathtt{\,\small\textbf+\,}}{\mathtt{2}}$$,the straight line L intersects the graph y=f(x) at M and N.The slope and the y-intercept of L are m and 1 respectively.

1)Express the y -coordinate of the mid-point MN in terms of m.

 

thank you 

 Nov 29, 2014

Best Answer 

 #1
avatar+128731 
+13

We can write L as

y = mx + 1

So, let us find the intersection of these two functions

mx + 1 = x^2 - 2x + 2

X^2 - 2x + 2 - mx - 1 = 0

x^2 -(2+m)x + 1 = 0

So, using the quadratic formula, we have

x = [( 2 + m) ± √[(2+m)^2 - 4]/2 = [(2 +m) ±√(m^2 + 2m)] /2

So, the y coordinates of M, N lie on line L and are given by

y1 = m[(2+m) + √(m^2 + 2m)] /2 + 1    and

y2 = m[(2+m) - √(m^2 + 2m)] /2 + 1 

Adding these two we have

[m[(2+m) + √(m^2 + 2m)] /2 + 1 ] + [ m[(2+m) - √(m^2 + 2m)] /2 + 1 ] =

[m(2 + m) + 2]

And dividing this by 2, we get the midpoint =

(m/2)(2 + m) + 1 =

(1/2)m^2 + m + 1

 

 Nov 29, 2014
 #1
avatar+128731 
+13
Best Answer

We can write L as

y = mx + 1

So, let us find the intersection of these two functions

mx + 1 = x^2 - 2x + 2

X^2 - 2x + 2 - mx - 1 = 0

x^2 -(2+m)x + 1 = 0

So, using the quadratic formula, we have

x = [( 2 + m) ± √[(2+m)^2 - 4]/2 = [(2 +m) ±√(m^2 + 2m)] /2

So, the y coordinates of M, N lie on line L and are given by

y1 = m[(2+m) + √(m^2 + 2m)] /2 + 1    and

y2 = m[(2+m) - √(m^2 + 2m)] /2 + 1 

Adding these two we have

[m[(2+m) + √(m^2 + 2m)] /2 + 1 ] + [ m[(2+m) - √(m^2 + 2m)] /2 + 1 ] =

[m(2 + m) + 2]

And dividing this by 2, we get the midpoint =

(m/2)(2 + m) + 1 =

(1/2)m^2 + m + 1

 

CPhill Nov 29, 2014
 #2
avatar+118613 
+8

That looked like a lot of work Chris :)

 Nov 29, 2014
 #3
avatar+128731 
+8

Yeah.....it seemed like too much.....I'm a little suspicious about my answer.....there's probably a more direct way to do it.......but my brain is too fried to want to think of another way!!!

 

 Nov 29, 2014

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