Check my working please? (1 Viewer)

[khorne]

From a multi-part question:

It asked to show, for some triangle:

a+b = 45
and a was larger than b

tanA * tanB = 1/9

9(tanA + tanB) = 8

Last part was hence find A and B: my working is below

tanA = 1/9tanB

9tanA + 9tanB = 8, thus, 9tanB = 8-9tanA

Sub back: tanA = 1/(8-9tanA)

-9tan^2A + 8tanA - 1 =0

or 9tan^2A - 8tanA + 1 = 0

thus, using quadratic formula:

(4 +/- sqrt[7])/9 = Tan A

So, being the larger of the two, tanA = (4+sqrt[7])/9

Is this all good? I was kind of hoping for a rational answer...

tanA = 1/

 

[Drongoski]

how do you get line 6 from line 5 ??

Shouldn't it be: 9(tan A + tan B) = 1

What was the original question ??

 

[khorne]

Fixed, it's a multiplication:

Original question is:

http://www.boredofstudies.org/courses/maths/3u/1999_Maths3_P_BurwoodGHS.pdf

Question 6B, part 3