Trigonometric

bonkysleuth SG

Diagram shows a L-shaped rod ABC where angle ABC = 90 deg, AB = 80 cm and BC = 60cm. It is hung from the ceiling at B such that CB makes an angle of deeter(?) with the ceiling. Points P and Q are 2 pointes on the floor which are vertically below A and C respectively. Given that deeter(?) varies,

state the range of PQ.

the (?) refers to spelling uncertainty. thanks.

jayh272416 SG

u mean theta.

min value is 60

max value is sqrt(60^2+80^2) = 100.

bonkysleuth SG

why is the minimum value 60?

Mikethm SG

"State" means no working is necessary.

Minimum occur when BC is against the roof, answer 60.

Maximum occur when AC parallel to PQ, answer 100.

anpanman SG

Nope, there is a definite method for this question. HintL Compare sin and cos graph. When sin graph is a maximum, cos graph is a minimum. From here, you can sub in the necessary values.

Eg. 80(0) + 60 (1) = 60 (minimum)

80(1) + 60(0) = 80 (cannot be minimum)

Mikethm SG

Nope, there is a definite method for this question. HintL Compare sin and cos graph. When sin graph is a maximum, cos graph is a minimum. From here, you can sub in the necessary values.

Eg. 80(0) + 60 (1) = 60 (minimum)

80(1) + 60(0) = 80 (cannot be minimum)

1st, we know that there is a definite method. However the question only ask for the answer and not the workings. So jay and me... just state as per the requirements of the question.

In addition,your suggested method defeated the purpose of learning the R formula. The appropriate technique to use here is the R formula.