Using the product to sum formula as shown here, we have

Note: and
— (1)
— (2)
— (3)
Using GC,

— (1)
— (2)
— (3)
Using GC,

Qn11
(i)

(ii) Since l is the common line of intersection on and , we need l to be on too. For that to happen,
1. l must be parallel to , that is, direction of l is perpendicular to normal to

2. Given that l is parallel to (since ), we need l to be on , so we need to be on

(iii)
For 3 planes to have nothing in common, then l must be parallel to (Note: if l is not parallel, l will cut at a point, which means that 3 planes will cut at a point)
from (ii)
But
12.
(i)

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