If `(1+sint)(1+cost)=5/4` then find the value of `(1-sint)(1-cost)dot`

Explanation

`(1+sint)(1+cost) = 5/4`

`=>1+sint+cost+sintcost = 5/4`

`=>(sint+cost) = 1/4-sintcost->(1)`

`=>(sint+cost)^2 = (1/4-sintcost)^2`

`=>sin^2t+cos^2t+2sintcost = 1/16+(sintcost)^2 -(sintcost)/2`

`=>1+sin2t = 1/16+(sin^2 2t)/4 - (sin2t)/4`

`=>16+16sin2t = 1+4sin^2 2t -4sin2t`

`=>4sin^2 2t -20sin2t -15 = 0`

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