Qualification > Math
IGCSE MATHS Doubts
Baladya:
Hey guys, i have this really annoying question that i m totally clueless with...
I was solving a question and the latest thing i could get to was: 21^2 = (2x)^2 + x^2 – (2)(2x)(x)(cos120). This is right in the mark scheme. Then what i do is : 441= 3x^2 +2x^2.(because i did cosine 120 times the answer of – (2)(2x)(x) which is -4x^2. And cosine 120 is -0.5... so (-0.5) (-4x^2)= 2x^2) And so its supposed to be 441=3x^2 + 2x^2.
However the asnwer in the mark scheme is 441= 7x^2.
From where the hell did the 7 come from?? plz help
(Answer of mark scheme: M1 212 = (2x)2 + x2 – 2.2x.x.cos120 oe
M1 441 = 7x2 )
The Golden Girl =D:
--- Quote from: Baladya on May 03, 2010, 01:53:37 pm ---Hey guys, i have this really annoying question that i m totally clueless with...
I was solving a question and the latest thing i could get to was: 21^2 = (2x)^2 + x^2 – (2)(2x)(x)(cos120). This is right in the mark scheme. Then what i do is : 441= 3x^2 +2x^2.(because i did cosine 120 times the answer of – (2)(2x)(x) which is -4x^2. And cosine 120 is -0.5... so (-0.5) (-4x^2)= 2x^2) And so its supposed to be 441=3x^2 + 2x^2.
However the asnwer in the mark scheme is 441= 7x^2.
From where the hell did the 7 come from?? plz help
(Answer of mark scheme: M1 212 = (2x)2 + x2 – 2.2x.x.cos120 oe
M1 441 = 7x2 )
--- End quote ---
i am confused , u gotta tell which question it is and where can i find it , so thati can answer
thx
Ghost Of Highbury:
--- Quote from: Baladya on May 03, 2010, 01:53:37 pm ---Hey guys, i have this really annoying question that i m totally clueless with...
I was solving a question and the latest thing i could get to was: 21^2 = (2x)^2 + x^2 – (2)(2x)(x)(cos120). This is right in the mark scheme. Then what i do is : 441= 3x^2 +2x^2.(because i did cosine 120 times the answer of – (2)(2x)(x) which is -4x^2. And cosine 120 is -0.5... so (-0.5) (-4x^2)= 2x^2) And so its supposed to be 441=3x^2 + 2x^2.
However the asnwer in the mark scheme is 441= 7x^2.
From where the hell did the 7 come from?? plz help
(Answer of mark scheme: M1 212 = (2x)2 + x2 – 2.2x.x.cos120 oe
M1 441 = 7x2 )
--- End quote ---
The bold part is correct.
This is what you got incorrect - "21^2 = (2x)^2 + x^2 – (2)(2x)(x)(cos120)."
If you solve the red part u get, (2x)^2 + x^2 = 4x^2 + x^2 = 5x^2. (Notice : it is (2x) the whole squared not 2x^2)
If u carry on, :- 5x^2 + 2x^2 = 7x^2.
Silly mistake, happens. No problem.
Vin:
hey guys jus wanted to ask what kind of calculators are allowed in the examination??
i use a Texas TI-30XB .. :) :)
Ghost Of Highbury:
We used. Fx - 991 Ms.
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