Warning: Illegal string offset 'html' in /home/hsn/public_html/forum/cache/skin_cache/cacheid_1/skin_topic.php on line 909

Warning: Cannot modify header information - headers already sent by (output started at /home/hsn/public_html/forum/cache/skin_cache/cacheid_1/skin_topic.php:909) in /home/hsn/public_html/forum/admin/sources/classes/output/formats/html/htmlOutput.php on line 114

Warning: Cannot modify header information - headers already sent by (output started at /home/hsn/public_html/forum/cache/skin_cache/cacheid_1/skin_topic.php:909) in /home/hsn/public_html/forum/admin/sources/classes/output/formats/html/htmlOutput.php on line 127

Warning: Cannot modify header information - headers already sent by (output started at /home/hsn/public_html/forum/cache/skin_cache/cacheid_1/skin_topic.php:909) in /home/hsn/public_html/forum/admin/sources/classes/output/formats/html/htmlOutput.php on line 136

Warning: Cannot modify header information - headers already sent by (output started at /home/hsn/public_html/forum/cache/skin_cache/cacheid_1/skin_topic.php:909) in /home/hsn/public_html/forum/admin/sources/classes/output/formats/html/htmlOutput.php on line 137

Warning: Cannot modify header information - headers already sent by (output started at /home/hsn/public_html/forum/cache/skin_cache/cacheid_1/skin_topic.php:909) in /home/hsn/public_html/forum/admin/sources/classes/output/formats/html/htmlOutput.php on line 141
Past paper 2005 noncalc Q9 - HSN forum

Jump to content


Past paper 2005 noncalc Q9


1 reply to this topic

#1 Sammie

    Top of the Class

  • Members
  • PipPipPipPipPip
  • 380 posts
  • Location:Glasgow
  • Interests:Stuff... mainly Fall Out Boy
  • Gender:Female

Posted 03 May 2008 - 01:03 PM

hello there strangers...slightly stuck and would totes love it if someone could help me.

"if cos 2x = 7/25 and 0<x<2pie find exact values of cosx and sinx"

I have this so far.

cos 2x= 7/25

since cos2x = 2cos^2x-1 then

2cos^2 x-1 = 7/25
2cos^2 x = 7/25 + 1 = 32/25
cos^2 x = 32/50


its going from there to the last step,how do I get rid of the square on the left hand side the SQa marking says cos x = 4/5 and sin x = 3/5 but I can't get it to come out right dry.gif

thanks peepsies <3
"Crowds are won and lost and won again, but our hearts beat for the diehards"

#2 antollo

    Showing Improvement

  • Members
  • PipPip
  • 10 posts
  • Gender:Female

Posted 18 May 2008 - 10:02 AM

you've done good to this point, now its just rearranging the equation, just watch your last step up there ^

2cos^2 x-1 = 7/25
2cos^2 x = 7/25 + 1 = 32/25

cos^2 x = 16/25 ( as 2cos^2 x = 32/25 , bring the 2 to the other side so you will divide here by 2 )
cos x = 4/5 ( square root your answer here )

now if you use ur trig triangles filling in that cos x = 4/5, you'll realise its a 3,4,5 triangle, therefore sin x = 3/5

wink.gif






1 user(s) are reading this topic

0 members, 1 guests, 0 anonymous users