Date | May 2016 | Marks available | 5 | Reference code | 16M.1.hl.TZ2.9 |
Level | HL only | Paper | 1 | Time zone | TZ2 |
Command term | Hence | Question number | 9 | Adapted from | N/A |
Question
Consider the equation √3−1sinx+√3+1cosx=4√2, 0<x<π2. Given that sin(π12)=√6−√24 and cos(π12)=√6+√24
verify that x=π12 is a solution to the equation;
hence find the other solution to the equation for 0<x<π2.
Markscheme
EITHER
LHS=√3−1√6−√24+√3+1√6+√24 M1
=√3−1√3−12√2+√3+1√3+12√2 A1
=2√2+2√2 A1
LHS=4√2⇒x=π12 is a solution AG
OR
LHS=√3−1√6−√24+√3+1√6+√24 M1
=(√3−1)(√6+√24)+(√3+1)(√6−√24)(√6−√24)(√6+√24) A1
=2√18−2√2 (or equivalent) A1
LHS=4√2⇒x=π12 is a solution AG
[3 marks]
√24(√3−1sinx+√3+1cosx)=2⇒sinπ12sinx+cosπ12cosx=2 M1
sinπ12cosx+cosπ12sinxsinxcosx=2 M1
sinπ12cosx+cosπ12sinx=2sinxcosx
sin(π12+x)=sin2x A1
π12+x=π−2x or π−(π12+x)=2x (M1)
x=11π36 A1
[5 marks]
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.
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 sinxcosx.