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3. Required the area of a field, in the form of a rhom
a boides, whose length AB is 42.5 perches, and perpendicular breadth CD is 32 perches. Fig. 15.
4. What is the area of a square tract of land, whose side measures 176.4 perches? Ans. 194A. IR. 36.96P.
5. What is the area of a rectangular plantation whose length is 52.25 chains, and breadth 38.24 chains?
Ans. 199A. 3R. 8.6P.
6. The length of a field, in the form of a rhombus, measures 16.54 chains, and the perpendicular breadth 12.37 chains: required the area. Ans. 20A. IR. 33.6P.
7. Required the area of a field in the form of a rhomboides, whose length is 21.16 chains, and perpendicular breadth 11.32 chains. Ans. 23A, 3R. 32.5P.
PROBLEM II. To find the area of a triangle when the base and perpen.
dicular height are given.
Multiply the base by the perpendicular height, and half the product will be the area. *
*DEMONSTRATION. A triangle is half a parallelogram of the same base and altitude (41.1.
1. The base AB of a triangular piece of ground, measures 12.38 chains, and the perpendicular CD 6.78 chains: required the area. Fig. 49.
9904 8666 7428
10)41.9682 Area, 4A. OR. 31P.
2. Required the area of a triangular field, one side of which measures 18.37 chains, and the distance from this side to the opposite angle 13.44 chains.
Ans. 12A. IR. 15P.
3. What is the area of a triangle whose base is 49 perches and height 34 perches? Ans. 5A. OR. 33P.
PROBLEM III. To find the area of a triangle when two sides and their
included angle are given.
EXAMPLES, 1. In a triangular lot of ground ABC, the side AB measures 64 perches, the side AC 40.5 perches, and their contained angle CAB 30°: required the area. Fig. 49.
* DEMONSTRATION. In the triangle ABC, Fig. 49. let AB and AC be the given sides, including the given angle A, and let CD be perpendicular on AB. Then by trig. rad. : sin. A:: AC:CD; but (cor. 1.6.) AC:CD :: AC X AB: CD X AB; therefore (11.5.) rad. : sin. A::AC X AB:CD X AB; but CD X AB is equal to twice the area
2. What is the area of a triangle two sides of which measure 15.36 chains and 11.46 chains respectively, and their included angle 47° 30? Ans. 6A. IR. 38P.
3. One side of a triangular field bears N. 12° E. distanice 18.23 chains, and at the same station the other adjacent side bears N. 78° 30. E. distance 13.84 chains: required the area. Ans. 11A. 2R. 11P.
4. Required the area of a triangular piece of ground, one side of which bears N. 82° 30'W. dist. 19.74 chains and at the same station, the other adjacent side S. 24° 15'E. dist. 17.34 chains. Ans. 14A. 2R. 8P.
PROBLEM IV. To find the area of a triangle when one side and the two
adjacent angles are given.
Subtract the sum of the two given angles from 180°,
opposite the given side,
* DEMONSTRATION. Let AB, Fig. 49, be the given side of the triangle ABC, and A and B the given angles; also let CD be perpendicular on AB: Then by trig.
sin. ACB : sin, B:: AB: AC
rad.: sin. A:: AC:CD. Therefore (C.6) rad. x sin. ACB : sin. A x sin. B :: AB X AC:CD X AC :: (cor. 1.6) AB: CD:: AB? : AB X CD; but AB X CD is equal to double the area of the triangle ABC; therefore (11.5) rad. x sin. ACB : sin. A x sin. B :: AB2: double the area of the triangle ABC,
EXAMPLES. 1. In a triangular field ABC, the side AB measures 76 perches, the angle A 60°, and the angle B 50°: required the area. Fig. 47.
The angle ACB = 180° - the sum of the angles A and B,
2. One side of a triangle measures 24.32 chains, and the adjacent angles are 630 and 74°; required the area.
Ans. 37A. OR. 22P. 3. What is the area of a triangular field, one side of which is 17.36 chains, and the adjacent angles 37° 30' and 48° 15'? Ans. 6A. 3R. 18P.
To find the area of a triangle, when the three sides are