# Trig Equation help

Printable View

• Dec 8th 2008, 06:41 PM
cokeclassic
Trig Equation help
hi I have a problem,

sin^2x = 6(cosx +1)

how do i solve and get answer pi/3, /3 etc.
• Dec 8th 2008, 06:48 PM
11rdc11
Quote:

Originally Posted by cokeclassic
hi I have a problem,

sin^2x = 6(cosx +1)

how do i solve and get answer pi/3, /3 etc.

$1 - \cos^2{x} = 6(\cos{x} + 1)$

$1 - \cos^2{x} = 6\cos{x} + 6$

$0 = \cos^2{x} + 6\cos{x} - 5$

Can you finish up from here?
• Dec 8th 2008, 06:49 PM
mr fantastic
Quote:

Originally Posted by cokeclassic
hi I have a problem,

sin^2x = 6(cosx +1)

how do i solve and get answer pi/3, /3 etc.

Start by substituting $\sin^2 x = 1 - \cos^2 x$.

Now re-arrange into a quadratic equation involving $\cos x$. Factorise and solve to get two equations for $\cos x$.

The only equation that leads to real solutions is $\cos x = 1$.
• Dec 8th 2008, 07:29 PM
cokeclassic
Ahh I had it right! I was looking at the wrong answer! (Lipssealed)
Thank you very much
{"found_math": true, "script_math_tex": 0, "script_math_asciimath": 0, "math_annotations": 0, "math_alttext": 0, "mathml": 0, "mathjax_tag": 0, "mathjax_inline_tex": 0, "mathjax_display_tex": 0, "mathjax_asciimath": 0, "img_math": 0, "codecogs_latex": 7, "wp_latex": 0, "mimetex.cgi": 0, "/images/math/codecogs": 0, "mathtex.cgi": 0, "katex": 0, "math-container": 0, "wp-katex-eq": 0, "align": 0, "equation": 0, "x-ck12": 0, "texerror": 0, "url": "http://mathhelpforum.com/pre-calculus/64010-trig-equation-help-print.html", "fetch_time": 1513102941000000000, "content_mime_type": "text/html", "warc_filename": "crawl-data/CC-MAIN-2017-51/segments/1512948517845.16/warc/CC-MAIN-20171212173259-20171212193259-00454.warc.gz", "warc_record_offset": 190431988, "warc_record_length": 2904, "token_count": 364, "char_count": 992, "score": 3.65625, "int_score": 4, "crawl": "CC-MAIN-2017-51", "snapshot_type": "longest", "language": "en", "language_score": 0.8658128976821899, "file_path": "/sailhome/yjruan/project/latent-lm/data/processed/finemath-4plus/finemath-4plus/train-00009-of-00064.parquet"}