How does the law of variable proportion affect the cost curve?

As we know law of variable proportion means as we increase the quantity of one input keeping other input fix... the Total physical product increase @ increasing rate than increase at decreasing rate than at decreasing rate.... and cost curve is totally dependent upon total variable cost curve.... so if the output is increasing this is due to increase in variable factors( labors) and if labors increase the cost will be obviously more as the labor increase....+