[Music]
in this video we're going to look at how
to expand double brackets
you should already know how to expand
single brackets but if you've forgotten
you may want to watch this video first
once we know how to expand double
brackets we'll also be able to expand
triple brackets and so on so we'll have
a look at a triple brackets example
towards the end of this video
let's get started with the double
brackets
remember that in algebra when two things
are next to each other
it means they are multiplied
so we need to multiply everything in the
second bracket but everything in the
first bracket
i am going to show you two methods and
then you choose whichever one you prefer
for the first method we draw arcs
linking each term
so x multiplied by x is x squared
x multiplied by 3 is 3x
negative 5 multiplied by x is negative
five x
and negative five multiplied by positive
three is negative fifteen
see how i've ended up with four arcs
that's really important because it means
i haven't missed anything out
some people like to remember this as
foil
first outer inner
last
the second method is by splitting up
each bracket into a grid
and then just multiply each bit together
x multiplied by x gives x squared
x times negative 5 is negative 5x three
times x is three x
and three times negative five is
negative fifteen
for both methods we then just need to
simplify the middle terms
by adding 3x and negative 5x to get
negative 2x
so that's our final answer
so here's one for you to do pause the
video expand the brackets and simplify
the answer click play when you're ready
did you get it right
here are two more questions for you to
do before we look at triple brackets
pause the video expand and simplify and
click play when you're ready
how did you get on
for the final answer it doesn't matter
which order you write the terms in
this could also have been written like
this
so let's end with triple brackets they
follow the exact same process as double
brackets
start by expanding the first two
brackets like you would normally
x squared plus 3x minus 5x
minus 15
and simplify it
now multiply this by the third bracket
make sure you simplify to get the final
answer
give this triple bracket a go pause the
video work out the answer and click play
when you're ready
did you get it right
so there we have expanding double
brackets and even triple brackets
we just need to remember to multiply
everything in the second bracket but
everything in the first bracket
so that we end up with four terms
and then we simplify it
in this video i showed you two different
methods so you choose which one you
prefer
[Music]