Math help

[Oreo]

Revising math, i have come across 2 things i can not do. Do not laugh, my Math is terrible.

The question in the revision book is "Factorise 2x^2 -7x -15". Now i can factorise, but this has thrown me

also, How do i find the line of symmetry on any given graph, in particular the graph of 2x^2 -7x -15.

Thanks

edit:

Also the question of, "Solve the simultaneous Equations"

y= x + 7
x^2 = Y^2 = 25

 

[Peter.Cort]

it factors to (2x^2 -10x+3x-15) --> (2x^2-10x) + (3x+15) --> (2x-3) + (x+5)

also since it's a parabola the line of symmetry is the vertex.

I'm gonna throw you for a loop here
f(x)=2x^2-7x-15
f'(x)= 4x-7
0=4x-7
4x=-7
x=-7/4

The line of symmetry on the graph of a parabola is going to be vertical so the slope is 1, so the equation for the line of symmetry of the graph 2x^2 -7x -15 is, y=x-7/4

hooray for calculus!

I dunno how to do it with lesser mathematics.

 

[Oreo]

1)it factors to (2x^2 -10x+3x-15) --> (2x^2-10x) + (3x+15) --> (2x-3) + (x+5)

also since it's a parabola the line of symmetry is the vertex.

2)
I'm gonna throw you for a loop here
f(x)=2x^2-7x-15
f'(x)= 4x-7
0=4x-7
4x=-7
x=-7/4

The line of symmetry on the graph of a parabola is going to be vertical so the slope is 1, so the equation for the line of symmetry of the graph 2x^2 -7x -15 is, y=x-7/4

hooray for calculus!

I dunno how to do it with lesser mathematics.

1) Thanks !
2) Oh so very confused what the heck you're on about

 

[Peter.Cort]

the second part i did with calculus, don't expect you to get it

I'm not sure how to do it like how you learned it.. It's been a while since I've done that stuff.

 

[Oreo]

Ohwell. How about that simultaneous equation ?


"y = x + 7
x^2 + Y^2 = 25

Solve it"

No idea where to start.

 

[Peter.Cort]

Well, the first equation is a line with slope 1, the second is a circle with the radius of 5. I'll look into what it wants.

 

[Oreo]

The question is asking for the value of X, and the Value of Y. If that's what you mean by "what it wants"

 

[Tim]

x^2 = Y^2 = 25

Ok, which one of those is meant to be a + symbol...?

 

[Peter.Cort]

ok, i remember what you have to do now.

y = x + 7
x^2 + Y^2 = 25

x^2 + x^2+14x+49=25
2x^2 + 14x + 24 = 0
x^2 + 7x + 12 = 0
x^2 + 3x + 4x +12 = 0
(x+4) (x+3) = 0
x = -3, -4

y = x + 7
1st Solution:
y=-3+7
y= 4
Point of Intersection at (-3,4)

2nd Solution
y=-4+7
y=3
Point of Intersection at (-4,3)

 

[Tim]

Aah, i forgot to divide by 2, i was gettin confused as well

Oreo, when they give you something like that, they want you to subsitute the small equation y = x + 7 into the big one x^2 + Y^2 = 25. That way you only have one unknown value

That leaves you with x^2 + (x+7)^2
Remember, when multiplying the (x+7)^2 out, it is not x^2 + 7^2
It is (x+7)(x+7)

Multiply that out and add it to the x^2, and that takes you to the begginings of Peter.Cort's workings