Question

(5+√11)(5-√11) Please help i give medals!
Answer choices:
A.36
B.14
C.25-10√11
D.25-√11

Answer 1

Hint: \(x^2 - y^2 = (x+y)(x-y)\)

Answer 2

What formula is that called? It's not the quadratic one is it?

Answer 3

It's the difference of two squares identity.

Answer 4

ugghh I'm not sure how to do that

Answer 5

Just observe the formula and fill in the blanks. What would x and y stand for in the case of \((5+\sqrt{11})(5-\sqrt{11})\)?

Answer 6

x would be 5 and y would be sqrt11, im not sure though. (sorry it took me so long to rrespond my computer shut down for an update and i had to switch to another computer.

Answer 7

Correct. Now apply that to \(x^2 - y^2\)

Answer 8

X would be 25 i think and if you squared a radical sign it should cancel leaving 11.

Answer 9

im not sure though

Answer 10

Correct.

Answer 11

However, x^2 = 25, not x = 25.

Answer 12

so thats the answer?

Answer 13

D

Answer 14

No.
x = 5, y = sqrt(11)
x^2 = 25, y = 11
We know that x^2 - y^2 = (x+y)(x-y)
So what is x^2 - y^2?

Answer 15

25-11=14

Answer 16

or do you have to square the 11 to?

Answer 17

No. It's asking y^2, not y.

Answer 18

so 121?

Answer 19

d because 11 cant be broken down and 5*5 is 25

Answer 20

@callie2240 Please read my solution.

@csimmons3 You must be very clear of what you are doing here. Back to first step: You defined x = 5 and y = sqrt(11), this doesn't change for the whole progress. The answer is x^2 - y^2, so you find x^2 and y^2 and substitute them into the equation. You don't magically transform y^2 into y - they stay two different (but related) numbers.

Answer 21

*substitute into the expression

Answer 22

i dont see a solution???

Answer 23

I'm lost

Answer 24

Ohhhh is it B?

Answer 25

Correct.

Next time you do math, in order to make yourself very clear about what you're doing, write variables and their values out. This way, you won't be confused.

@callie2240 See all my posts for details.

Answer 26

Thanks for all the help :)

Answer 27

i saw thanks

Answer 28

it would be B