See in the ques it is written in a parallelogram! In particular , In this case Let us consider the parallel lines L1 and L3. Here coefficient of x of L1=coefficient of x of L3 and coefficient of y of L1=coefficient of y of L3…!! The only difference is in constant terms of L1 and L3…!
Similarly If we consider the parallel lines L2 and L4. Here also coefficient of x of L2=coefficient of x of L4 and coefficient of y of L2=coefficient of y of L4…!! The only difference is in constant terms of L2 and L4…!
Whenever u find this situation where the only difference is in constant terms for parallel lines then u can use this method-
Equation of diagonal BD is given by L_1L_4-L_2L_3=0 and similarly AC is given by L_1L_2-L_3L_4=0(method for any parallelogram and i used this method)
But there is another method too to find the equation of diagonals in case the parallelogram is a particular parallelogram(the parallelogram which i mentioned above that is there should be only difference in constant terms for parallel sides) then equation of BD is given by L_1-L_2=0 or L_4-L_3=0.