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Date May 2016 Marks available 3 Reference code 16M.1.hl.TZ2.9
Level HL only Paper 1 Time zone TZ2
Command term Verify Question number 9 Adapted from N/A

Question

Consider the equation 31sinx+3+1cosx=42, 0<x<π231sinx+3+1cosx=42, 0<x<π2. Given that sin(π12)=624sin(π12)=624 and cos(π12)=6+24cos(π12)=6+24

verify that x=π12x=π12 is a solution to the equation;

[3]
a.

hence find the other solution to the equation for 0<x<π20<x<π2.

[5]
b.

Markscheme

EITHER

LHS=31624+3+16+24LHS=31624+3+16+24    M1

=313122+3+13+122=313122+3+13+122    A1

=22+22=22+22    A1

LHS=42x=π12LHS=42x=π12 is a solution     AG

OR

LHS=31624+3+16+24LHS=31624+3+16+24    M1

=(31)(6+24)+(3+1)(624)(624)(6+24)=(31)(6+24)+(3+1)(624)(624)(6+24)    A1

=21822=21822 (or equivalent)     A1

LHS=42x=π12LHS=42x=π12 is a solution     AG

[3 marks]

a.

24(31sinx+3+1cosx)=2sinπ12sinx+cosπ12cosx=224(31sinx+3+1cosx)=2sinπ12sinx+cosπ12cosx=2    M1

sinπ12cosx+cosπ12sinxsinxcosx=2sinπ12cosx+cosπ12sinxsinxcosx=2    M1

sinπ12cosx+cosπ12sinx=2sinxcosxsinπ12cosx+cosπ12sinx=2sinxcosx

sin(π12+x)=sin2xsin(π12+x)=sin2x    A1

π12+x=π2xπ12+x=π2x or π(π12+x)=2xπ(π12+x)=2x     (M1)

x=11π36x=11π36    A1

[5 marks]

b.

Examiners report

This question proved to be the most problematic question in the paper.

Part (a) was generally well done, with competent fraction and surd manipulation seen successfully in leading to the given answer.

a.

This question proved to be the most problematic question in the paper.

The number of scripts seen where part (b) was tackled with complete success numbered in the single figures; solutions were rarely if ever seen. Some candidates scored one mark by finding, or using, the common denominator sinxcosxsinxcosx.

b.

Syllabus sections

Topic 3 - Core: Circular functions and trigonometry » 3.6 » Algebraic and graphical methods of solving trigonometric equations in a finite interval, including the use of trigonometric identities and factorization.
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