Plz help!! Maths (1 Viewer)

[Mohit7]

how do Solve a question like:

Find any x values for which the gradient to the tangent to the curve
y=x^{[FONT=&quot]2 [/FONT]}[FONT=&quot]-3x-1 is parallel to the x-2y-1=0[/FONT]

Thanks

^{[FONT=&quot]
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[Dark Phoenix]

im not sure if this is right, but anyway:

Put x-2y-1=0 into y = mx + b form and ull find that m is 1/2

Now differentiate y=x2 -3x-1 and ull get 2x - 3 (this is the gradient of the curve at a certain point

Then is think u get 1/2 = 2x - 3

and x = 7/4

dont take me word for it though. hope i helped

 

[muttiah]

one is a parabola.. the other is straight line.. in the straight line make y the subject and u'll get m=1/2

for the parabola..differentiate it



so u know that to b parallael m1=m2

so the straight line has gradient 1/2
and the parabola has to have gradient half
so 2x-3 = 1/2 and solve and u will get the x value

 

[airie]

Bleh, calculus...

You could use the discriminant of quadratics too. As above, find the gradient of the line to be 1/2, therefore the tangent is of the form y=0.5x+b where b is a real number. Solve simultaneously with y=x²-3x-1, you get x²-3.5x-(b+1)=0. Since the line is a tangent to the parabola, there exists only one point of contact ie. one solution to the equation, therefore the discriminant equals zero. You can then solve for x

 

[ronaldinho]

u know how to do every question ^ :S

 

[SoulSearcher]

That's because she's damn good at maths, and she knows it :uhhuh: