Cosine Rule - Side length intro SACHS
Cosine Rule - Side length
Step one: To calculate amissing side c, you need 2sides and the includedangle. e.g. a, b & C.
c2 = 42 +         2 – 2 x 4 x        x cos          o
Step 2: Sub in the values
for a, b and C.
c2 =
c2 = 42 + 72 – 2 x 4 x 7 x cos 138o
Step 3: Enter into the
calculator.
Correct to 1 d.p., but
leave all decimal places
on your screen.
Correct to 1 d.p.
c2 = 106.6.....
c =
Step 3: Get the square
root of your answer to get
c by itself.
cm
c2 = 17.32 +           2 – 2 x 17.3 x           x cos          o
Now, complete the steps
without instructions
c2 = 17.32 + 11.52 – 2 x 17.3 x 11.5 x cos 118o
c2 =
Correct to 1 d.p., but
leave all decimal places
on your screen.
c2 = 618.3.....
Correct to 1 d.p.
c =
m
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