<p>I want to solve this system of equations for x.
x^2 - y^2 = 77 and 2x - 3y = 5</p>
<p>When I enter
solve(x^2 - y^2 = 77 and 2x - 3y = 5,{x,y})
it says that x = -14.15 or 10.15</p>
<p>But when I just solve it by hand, I get 9.73 or -13.7 (which is also what my book gets). Why is that? Am I entering it incorrectly in my calculator??</p>
<p>Thanks :)</p>
<p>haha, I did scroll to the right. That’s how I got those two solutions… and there obviously aren’t more than two.</p>
<p>what type of calculator are you using?</p>
<p>TI-89 Titanium</p>
<p>Commissars used to lead the masses into combat. Nowadays they just manipulate the masses (see the first post or “[Commissar</a> readies the attack”](<a href=“http://www.lshmwaco.org/albums/Mad_baron/photos/photo4.html]Commissar”>Commissar readies the attack)). 
Glitches in a book (SparkNotes?) should not be impedimental.
You could’ve plugged your and TI’s x and y in both equations and see which values work better. (You are right - scrolling does not cut it.) 
</p>
<p>You may not trust your doctor, but you should trust your calculator!
I suspect that what you (and a poor book author) did by hand was getting from
x^2 - ((2x-5)/3)^2 = 77 to
5x^2 +20x + 25 = 693 instead of
5x^2 + 20x - 25 = 693.</p>
<p>Try this on your trustworthy TI:
Set “Exact/Approx” MODE to “AUTO”.
Define y = (2x - 3)/5 (use F4 and 1),
x^2 - y^2 - 77 = 0
“ENTER”
solve(
“UP arrow”
“ENTER”
“,x)”
“DIAMOND”
“ENTER”.</p>
<p>Don’t forget to clean up your room with F6.</p>
<p>This should help (I hope). ;)</p>
<p>Instead of
Define y = (2x - 3)/5
you can
solve(2x - 3y = 0, y).</p>
<p>OK, here’s what I entered (and I think that’s what you meant):</p>
<p>solve(y=(2x-5)/3 and x^2+y^2-77=0,x)</p>
<p>And it just says “false” 
… what does that mean?</p>
<p>When you did
it gave you the right answer.</p>
<p>When solving by hand, after you plugged
y = (2x-5)/3
in
x^2 - y^2 = 77,
you most likely got
5x^2 + 20x + 25 = 693, or
5x^2 + 20x - 668 = 0
with x= 9.73 or -13.7.</p>
<p>It should be
5x^2 + 20x - 25 = 693, or
5x^2 + 20x - 718 = 0
with x = -14.15 or 10.15</p>
<p>Second part of my post just illustrates solving the system step by step.
Oops, I just noticed my mistype “solve(2x - 3y = 0, y)” in post #6.</p>
<p>Let’s start again:
solve(2x - 3y = 5, y)
[F4] 1
[Up Arrow key]
[ENTER]
[ENTER]</p>
<p>You see y=(2x-5)/3 (don’t type this line :)).</p>
<p>x^2 - y^2 - 77 = 0
[ENTER]</p>
<p>You see (5x^2)/9 + (20x)/9 - 718/9 = 0 (don’t type this line either :D).</p>
<p>solve(
[Up Arrow key]
[ENTER]
,x)
<a href=“to%20get%20an%20approximate%20answer”>DIAMOND key</a>
[ENTER]</p>
<p>That’s all.
I am not sure why you are getting
It’s possible that you mistyped something and got a quadratic equation with no real solutions, like in
solve(x^2 = -1, x).</p>
<p>To start from the scratch, do [F6] 2 first.</p>
<p>“5 more practice tests for the SAT II Math IIC”, Test 3, #33.
All the answer choices are wrong, and the mistake in solution is exactly the one I described.</p>
<p>I don’t know an SAT prep book without mistakes or typos, and SparkNotes SAT II books have little of them. Overall value of these books outweighs their shortcomings.</p>