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The ways to complete the first one is to realise that it involves a difference of two squares. If you were to see (X^2) with a constant (number), you know they have no factor in common, meaning the two te...

y² + 2xy dy/dx = 3cos(3x) + 1/y - x/y² dy/dx                   thereforedy/dx = (3cos(3x) + 1/y - y²​​​​​​) / (2xy + x/y²)

Perimeter= 72Ratios are 3:4:5In total, you can think of there being 3+4+5=12 "portions".This means that in the perimeter includes 12 portions. 72/12=6 so each portion is worth 6cm.
Now we c...

When I am expanding brackets I use the acronym FOIL and simplify. You begin by multiply the first term (F) in each bracket, followed by multiplying the outside terms (O), then the inside terms (I) and fin...

cos(2x) = 2cos²(x) - 1 This is the identity. Therefore we can substitute in 2[cos²(x)] to be 2 multiplied by (1/4)².Therefore cos(2x) = 2(1/4)(1/4) - 1 = 2/16 - 1 = 2/16 -...