Maths Unit C

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  • Created by: kirsty
  • Created on: 11-06-13 11:52
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  • Maths Unit C
    • Direct and inverse proportion
      • Inverse
        • y   1/x read as 'y is inversely proportional to x'
          • example y=5 when x=4 5=m/4  5x4=m=20 y=20/x
            • further examples: find y when x=30 y=20/30=0.6 find x when y=25  25=20/x x=20/25=0.8
      • Direct
        • y   x   read as 'y is directly proportional to x'
          • example: y=1.8 x=9 y=mx 1.8=mx9 1.8/9=m=0.2 y=0.2x
            • further examples: find y when x=52 y=0.2x52 =10.4          find x when y=42   42=0.2 * x 42/0.2=x=210
    • percentage increase and decreases
      • Increase
        • 100%+ (the percentage increase) then that number x by original amount
          • Example: Julie is given a pay rise of 3.5% on her current salary of 34900 so: 100%+3.5%= 103.5% 34900x103.5 = 36121.50
      • Decrease
        • 100%-(the percentage decrease) then this number x by original amount
          • example: work out the new price of a camera that did cost £480 before the 22% reduction so: 100%-22%= 78% 480x0.78=£374.40
    • circles
      • circumferene  = pie x diameter
        • example=  pie x 8 = 8pie= 25.13274123
      • area = pie x r squared
        • example pie x 4 squared = 16 pie = 50.26548246
          • for sectors for both area and circumference you just do the angle of the sector divided by 360 and then the same as you did for the others.
      • cherry pies delicious! apple pies are too!
    • Factorising
      • examples: PQR+RST = R(PQ+ST) 4XY-8X = 4(XY-2X) 2A+2B = 2(A+2B)
        • factorising a x"+4x+3=0 you would get (x+3) and (x+1) this is because the numbers add to make the middle and times to make the end number.
      • expanding:  4(5a+2) = 20a +8   3x(2-9y) = 6x-9xy 3(2x+5) = 6x+15
        • when cant factorise use the quadratic formula!
  • y   1/x read as 'y is inversely proportional to x'
    • example y=5 when x=4 5=m/4  5x4=m=20 y=20/x
      • further examples: find y when x=30 y=20/30=0.6 find x when y=25  25=20/x x=20/25=0.8
  • for surface areas you add the area of each surface altogether,

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