CHAPTER 7
Solutions of Triangles
20
=
4
x
2
8
+
x
2
–
5
x
2
4
•
8
(
4
X
¡
2
X
=
SHIFT
cos
-1
cos
=
5
•
ABC
is a triangle in which
AB
= 4cm,
AC
= 5.4cm and
BC
= 8cm. Find
ACB
∠
.
OPERATION
1
. Use the formula
BC
AC
AB
BC
AC
ACB
×
×
−
+
=
∠
2
cos
2
2
2
to determine
ACB
∠
cos
. Ensure
calculator is in
COMP/Deg
mode.
ACB
∠
cos
= 0.893055555.
2
. To determine
ACB
∠
, press
Hence,
ACB
∠
is approximately 26.74°.
Answers to Quick Check 1
1
(a)
-381.078125
(b)
5/42
(c)
210,034.1658
2
(a)
0.034899496
(b)
1
(c)
2
3 (a)
7,079.457844
(b)
2.724069927
(c)
21.10019602,@
0.368267893
4
755.0922277
5
1,096.633158
6
-12.05796327
7
(a)
1.966637001
(b)
4.289146637
(c)
11.35402128
8 (a)
178°11’23.5’’
(b)
133°41’24.5’’
(c) -
166°9’27.94’’
9
°
1
.
0
cos
10
5.595526906
Answers to Quick Check 2
1
(a)
43,758
(b)
55,440
(c)
362,880
2
5, 10, 13
3 (a)
1,951
(b)
65.03333333
(c)
19.78633086
4
0.201653658
5
95,040
6
11,400
7
(a)
35.73496445°
(b)
0.9125573
Example 3
5.4
2
+8
2
-4
2
77.16
Ans
¡
(2 X5.4 X8
0.893055555
cos
-1
Ans
26.74024593
8cm
4cm
5.4cm
B
C
A