When I want to trick my students to solve a system of equations like this. Lucky for you there is a quick and easy way to overcome it. In this video I will show you how.
so here's one of the most obvious ways
that students get mixed up on a problem
like this and what they do is they just
go and apply like either elimination
without looking at if the variables are
going to be aligned now if you're doing
substitution that's a little bit
different story because you're just
isolated in a variable and then plugging
it into the other equation but I only
like to do substitution when I already
have a variable isolated and you can see
in this case we don't have that so what
I'm going to want to do is use the
elimination method now you can recognize
here that in my top equation I have you
know 2x plus 3y equals 7 but in my
bottom equation I have a 5y minus 1
equals 2x right so they're not aligned
and remember when you're applying
elimination you're either just adding or
subtracting two equations vertically so
there's no one way to have them like
perfectly aligned or like the perfect
way should X and then y or should do y
and then X but a kind of like a general
rule of thumb is just to kind of follow
the standard form
and again this is not a perfect solution
for everything but I think in this
equation you can see that the top
equation is in that standard form so
what I'm going to do is I'm going to go
ahead and rewrite my bottom equation so
therefore it can be in that format now
to do that what I'm simply going to need
to do is subtract the 2x on both sides
as well as add the 1 to both sides
okay so now you can see what I have is
everything vertically aligned and that's
really important because in this case
this problem is actually really really
simple right it's very obvious a lot of
students will make this mistake because
they won't think or maybe there's a time
sensitive test going on and you know
it's kind of like one of those like
mental farts that go on and we're like
oh crap you know what am I doing like
let's quickly do this and they sometimes
just over Overlook it or they forget it
it's one important thing that I really
really want you to make sure you're
paying attention to especially when
you're doing elimination is make sure
everything is vertically aligned and if
it's not vertically aligned like it's
not bad it's not hard to go ahead and
rearrange it but it's essential for you
to be able to do that and the nice thing
that's really important about this is do
you notice that my exes already like set
up perfectly for elimination right I
have the exact same coefficient for my X
once positive and one's negative so
therefore in this equation I can simply
just add these two equations up
vertically so 2x minus a 2X is going to
be a 0x which is just 0. 3y plus a 5y is
going to be an 8y and 7 plus 1 is going
to equal an eight now I can just divide
by eight on both sides and Y is equal to
one now remember we still need to finish
this equation and in this example it
doesn't really matter which equation
we're going to plug in for y I will say
this probably this top equation before I
actually had to manipulate it was
probably not too bad to go ahead and
plug in you know a one and two to go
ahead and solve for I'm sorry to solve
for x right because I already have this
x almost all by itself so all I simply
need to do is plug in the 1 in for the Y
and now all I simply need to do is go
ahead and simplify this to go ahead and
solve for y
and there you go once you have
everything aligned you're all set to go
ahead and solve for x as well as to
solve for y