Algebra starts with x and then we add arithmetical numbers, 1,2,5.1,a,b,c to it and get expressions like
And also 2x+3, 3x-2 and so on & so forth
Straight Lines are the starting concept in Coordinate Geometry. It incorporates Algebra, Geometry and Trigonometry in good measure.
So, if you are good at the basic concepts of geometry and trigonometry and know how to apply the same in a right angled triangle, straight lines become easy.
Starting with the basic equations of a straight line we go on to examine higher levels of problems including IIT level problems